Electroplating bath, method for manufacturing plated product, and plated product

ABSTRACT

An electroplating bath is configured to precipitate a black trivalent chromium layer onto an object to be plated. The electroplating bath includes a nanodiamond and a thiocyanate ion as color enhancers.

BACKGROUND 1. Field

The present disclosure relates to an electroplating bath for obtaining a black plated product with a reduced yellowish color, a method for manufacturing a plated product, and a plated product.

2. Description of Related Art

Plating treatment is generally carried out as one of the surface treatment techniques for decorative parts to impart appearance characteristics such as decorativeness of decorative parts including plastics, metals, glasses, and ceramics, and functionalities such as durability. In such plating treatment, a chromium plating layer having a metal-like appearance has a plating film with high hardness and accordingly good appearance characteristics and functionalities, and thus is used as, for example, a finishing uppermost plating layer with copper plating or nickel plating as a base.

In recent years, a demand for rich jet-black appearance has been increasing from the viewpoint of design, and for this reason, a trivalent chromium plating treatment is sometimes applied to products for vehicles. Products to which trivalent chromium plating is applied as disclosed in, for example, Japanese Laid-Open Patent Publication No. 2017-106119 have been conventionally known. The same patent publication discloses the use of a trivalent chromium plating solution having the thiocyanate ion and colloidal silica as color enhancing additives. A jet-black specular appearance enhances its color tone when a color enhancing additive such as colloidal silica is blended into a trivalent chromium plating solution.

However, the products in which the trivalent chromium plating disclosed in the above patent publication is used have the problem of having a strong yellowish color (b* value) in the obtained black plating film, whereby the product marketability is impaired.

SUMMARY

An objective of the present disclosure is to provide an electroplating bath that reduces a yellowish color in a black plated product, a method for manufacturing a plated product, and a plated product.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In accordance with a first aspect of the present disclosure, an electroplating bath is provided that is used to precipitate a black trivalent chromium layer onto an object to be plated. The electroplating bath includes a nanodiamond and a thiocyanate ion as color enhancers.

In accordance with a second aspect of the present disclosure, a method for manufacturing a plated product having a black trivalent chromium plating film is provided. The method includes: forming a black trivalent chromium plating film onto an object to be plated by electroplating using the above-described electroplating bath; and applying a chromate treatment onto the black trivalent chromium plating film.

In accordance with a third aspect of the present disclosure, a plated product is provided that has a black trivalent chromium plating film in which nanodiamond particles are dispersed. A b* value of a surface of the plated product is four or less.

DETAILED DESCRIPTION

This description provides a comprehensive understanding of the methods, apparatuses, and/or systems described. Modifications and equivalents of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted.

Exemplary embodiments may have different forms, and are not limited to the examples described. However, the examples described are thorough and complete, and convey the full scope of the disclosure to one of ordinary skill in the art.

First Embodiment

Hereinafter, an electroplating bath according to a first embodiment of the present disclosure will be described. The electroplating bath of the first embodiment is an electroplating bath for precipitating a black trivalent chromium layer onto an object to be plated, and contains trivalent chromium with nanodiamond and a thiocyanate ion as color enhancers.

The thiocyanate ion is blended to obtain a black appearance in plated products. The concentration of the thiocyanate ion in the electroplating bath is not particularly limited, and is preferably 0.5 g/L to 10 g/L, and more preferably 0.5 g/L to 3 g/L. When the concentration of the thiocyanate ion is 0.5 g/L or more, a black plating appearance with a more favorable color shade is obtained. In particular, when used with the nanodiamond, a jet-black appearance with a reduced yellowish color and lightness is obtained. When the concentration of the thiocyanate ion is 10 g/L or less, a black plating appearance with a more favorable color shade is efficiently obtained. The thiocyanate ion can be blended in the form of sodium thiocyanate, potassium thiocyanate, or the like.

Nanodiamond is blended to obtain a jet-black specular appearance with a reduced yellowish color in plated products. The concentration of the nanodiamond in the electroplating bath is not particularly limited, and is preferably 0.01 to 5 g/L, more preferably 0.02 to 0.16 g/L, and further preferably 0.05 to 0.15 g/L. When the concentration of the nanodiamond is 0.01 g/L or more, a yellowish color and lightness is reduced and a better jet-black specular appearance is obtained. When the concentration of the nanodiamond is 5 g/L or less, the dispersibility of nanodiamond particles is enhanced and a jet-black specular appearance with a reduced yellowish color and lightness is efficiently obtained.

The nanodiamond usable has a primary particle size of less than 1 μm (nanolevel), preferably 100 nm or less, and more preferably 10 nm or less. Additionally, it is preferable to use highly dispersible nanodiamond with reduced primary particle aggregation from the viewpoint of obtaining a good black appearance with a reduced yellowish color and lightness. Alternatively, a commercial product may be used, and, for example, uDiamond (primary particle 4 to 6 nm, high dispersion grade) manufactured by Carbodeon can be used.

For the trivalent chromium, a trivalent chromate is used. Specific examples of the trivalent chromate is not particularly limited as long as it is a component publicly used for forming a trivalent chromium plating film, but examples include chromium sulfate, chrome alum, chromium nitrate, chromium chloride, and chromium acetate. These components may be used singly, or two or more may be used in combination. The concentration of the trivalent chromium in the electroplating bath is not particularly limited, but is preferably 1 to 100 g/L, and more preferably 10 to 50 g/L, from the viewpoint of providing a good black color tone and stability of the electroplating bath.

Known additives typically used in the electroplating in which trivalent chromium is used, such as a complexing agent, a conductive salt, a pH buffer, a precipitation promoter, a humectant, a catalyst, an organic substance, a leveling agent, a brightener, and a reducing agent, can be suitably used. Within a range which does not inhibit the advantages of the present disclosure, other additives that control plating reactions and colors may be used. Examples of the complexing agent include potassium formate and sodium malate. Examples of the conductive salt include ammonium chloride, sodium chloride, potassium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate. Examples of the pH buffer include boric acid, formic acid, and acetic acid. Examples of the humectant include nonionic surfactants such as sodium lauryl sulfate, sodium ethylhexyl sulfate, and polyoxyethylene alkylphenyl ether. Examples of the other additives which control plating reactions and colors include silica, sulfur, phosphoric acid, and saccharine. An amount of each component used can be suitably adjusted and added depending on various purposes.

An object (substrate) to be plated to which the electroplating bath of the first embodiment is applied is not particularly limited, and a known material, as long as it is an electroplatable object, can be suitably selected depending on the purpose. Examples of the substrate include, other than metals, plastics, glasses, and ceramics with the surface coated with a conductive material. The substrate made of a plastic can be suitably selected in consideration of functionalities such as hardness, workability, heat resistance, and platability and the purpose of use. Examples of the plastic include acrylonitrile-butadiene-styrene (ABS) copolymers, polycarbonate (PC) plastics, PC/ABS alloys (PC/ABS blend plastics), polypropylene (PP) plastics, polyacryl plastics (polymethacryl plastics), polymethylmethacrylate (PMMA) plastics, modified polyphenylene ether (PPE) plastics, polyamide plastics, and polyacetal plastics. The substrate made of a plastic can be molded using a known molding method such as the injection molding method, the extrusion molding method, the blow molding method, or the compression molding method. Examples of the metal used for the substrate include irons, stainless steels, aluminums, aluminum alloys, titaniums, and titanium alloys. These substrates may be selected and used singly, or more than one kind may be used in combination.

When the substrate surface is coated with a conductive material, copper plating or nickel plating may be employed from the viewpoint of providing good appearance characteristics and functionalities. The copper plating may be formed by an electroless copper plating treatment or an electrolytic copper plating treatment. These can be suitably selected depending on the characteristics of each plating. When an electrolytic copper plating treatment is applied, it is preferable to apply an electroless plating treatment for imparting the conductivity to the substrate surface. Examples of the electroless plating treatment include, other than the electroless copper plating treatment, an electroless nickel plating treatment.

A known method can be suitably employed for the electroless copper plating treatment. Examples include a formaldehyde bath in which formaldehyde is used as a reducing agent. Also, the treatment can also be carried out by a bath which uses, as a reducing agent, borohydrides such as potassium tetrahydroborate, dimethyl aminoborane (DMAB), and sodium borohydride, glyoxylate, hypophosphite, phosphinate, cobalt(II) salt, and hydrazine. For example, the treatment, when carried out by the formaldehyde bath, can be carried out by immersing the substrate into a plating bath containing, other than the formaldehyde as the reducing agent, copper sulfate as the copper salt, Rochelle salt and ethylenediaminetetraacetic acid (EDTA) as complexing agents, a pH adjusting agent, a stabilizer, a promoter, a coating modifier, and a surfactant.

A known method can be suitably employed for the electroless nickel plating treatment. For example, when an ABS plastic is used as the substrate, the substrate is immersed into a surfactant-containing bath to degrease the substrate surface and subsequently immersed in a chromic acid/sulfuric acid solution to carry out an etching treatment onto the substrate surface. Then, a catalyst represented by a Pd/Sn mixed colloid catalyst or the like is deposited on the substrate surface to activate and subsequently the electroless nickel plating treatment is carried out. The electroless nickel plating treatment can be carried out by immersing the substrate in a plating bath containing phosphinate, tetrahydroborate salt, DMAB, or hydrazine as a reducing agent, nickel sulfate or nickel chloride as a nickel salt, together with a complexing agent, a promoter, a stabilizer, a pH adjusting agent, and a surfactant.

A known method can be suitably employed for the electrolytic copper plating treatment. For the plating bath, for example, any of a copper cyanide plating bath containing copper(I) cyanide and sodium cyanide, a copper pyrophosphate plating bath containing copper pyrophosphate and potassium pyrophosphate, or a copper sulfate plating bath containing copper sulfate may be employed. In the plating bath, known additives such as a leveling agent, a promoter, and an inhibitor can be blended. These additives can be added by suitably adjusting the amounts blended and ratios depending on surface conditions of the substrate such as surface roughness and waviness.

Further, for a base layer of the substrate to which the electroplating bath of the first embodiment is applied, a nickel plating treatment such as semi-bright nickel (SBN) plating treatment, a bright nickel (BN) plating treatment, a dull nickel (DN) plating treatment, or a microporous nickel plating treatment, may be applied to the above copper plating layer. These nickel plating layers reduce the corrosion and thus improve the durability of plated products.

A known method can be suitably employed for the nickel plating treatment. More specifically, examples include methods that use a Watts bath, an all-chloride bath, a sulfamate bath, and a wood's strike bath. To the plating bath, a known brightener applicable to a nickel plating treatment may be blended from the viewpoint of imparting brightness to a nickel plating layer.

Conventionally known conditions can be employed for the method for precipitating a black trivalent chromium plating layer onto the surface of an object to be plated by a trivalent chromium plating treatment using the electroplating bath of the first embodiment. For example, the method can be carried out under the conditions of a pH range from 2.5 to 4.5, a bath temperature range from 30 to 50° C., and a current density range from 1 to 20 A/dm², of a plating bath.

Next, operation of the electroplating bath of the first embodiment configured as above will be described below.

In the electroplating bath for precipitating a black trivalent chromium layer onto an object to be plated of the first embodiment, nanodiamond is blended as a color enhancer. Accordingly, a plated product obtained using such an electroplating bath obtains a jet-black appearance with a reduced yellowish color. It is presumed that the nanodiamond has a low transmittance compared with colloidal silica that has been conventionally used and thus can reduce an input reflected yellowish color thereby reducing a b* value.

The electroplating bath of the first embodiment has the following advantages.

(1) In the electroplating bath for precipitating a black trivalent chromium layer onto an object to be plated of the first embodiment, nanodiamond is blended as a color enhancer. Accordingly, a plated product obtained using such an electroplating bath obtains a jet-black appearance with a reduced yellowish color. Further, a thiocyanate ion is blended as a color enhancer. Accordingly, the plated product obtains a jet-black appearance with a reduced lightness.

(2) When the concentration of the nanodiamond ranging from 0.02 to 0.16 g/L is employed, a yellowish color and lightness is reduced, enabling the obtainment of a richer jet-black specular appearance. Additionally, the dispersibility of nanodiamond particles is enhanced and thus a jet-black specular appearance with a reduced yellowish color and lightness is efficiently obtained.

Second Embodiment

Hereinafter, a plated produce according to a second embodiment of the present disclosure will be described. Differences from the first embodiment will mainly be described. The plated product of the second embodiment is a plated product having a black trivalent chromium plating film in which nanodiamond particles are dispersed and a b* value of the surface of the plated product is four or less. A b* value of the surface of the plated product can be measured using a spectrophotometer (e.g., manufactured by Konica Minolta, Inc.: CM-700D).

Further, the plated product of the second embodiment preferably has an L* value of the surface of fifty or less. With such a characteristic feature, the black trivalent chromium plating film obtains a richer jet-black appearance.

A method for manufacturing the plated product of the second embodiment can be preferably carried out using the electroplating bath of the first embodiment.

Specifically, the above plated product is obtained by a step of forming a black trivalent chromium plating film by electroplating onto an object to be plated using the plating bath of the first embodiment. For plating conditions, those described in the first embodiment section can be employed. When the requirement for an L* value of the plated product surface of fifty or less is met, it is preferable for the concentration of the nanodiamond in the electroplating bath to be set in a range from 0.02 to 0.16 g/L.

For an object to be plated, those described in the first embodiment can be employed. An object to be plated may have copper plating or nickel plating applied as a base plating treatment before applying a trivalent chromium plating treatment from the viewpoint of easily obtaining a plated product that meets the requirement of the second embodiment. Examples of the nickel plating treatment include a semi-bright nickel (SBN) plating treatment, a bright nickel (BN) plating treatment, a dull nickel (DN) plating treatment, and a microporous nickel plating treatment. It is preferable that, for example, copper plating, semi-bright nickel plating, bright nickel plating, and microporous nickel plating be sequentially applied to a substrate composing an object to be plated.

Additionally, it is preferable that a chromate treatment is further applied to a black trivalent chromium plating film to form a chromate film. When such a treatment is applied, a plated product having a black trivalent chromium plating film in which nanodiamond particles are dispersed obtains a jet-black appearance with a more reduced yellowish color (b* value) and lightness (L* value).

A known method can be suitably employed for a chromate treatment.

Examples of the chromate treatment include the electrolytic chromate method and the immersion chromate method. Examples of the electrolytic chromate include a method in which ECR500 (manufactured by JUC) is used as an electrolyte and electrolysis is carried out at 50 to 60° C. for 1 to 2 minutes at a current density of 0.5 A/dm². The immersion chromate method is carried out by the immersion in a chromic acid bath. Examples of a solution composition for the chromic acid bath include those having a chromic acid or a sodium dichromate as a main component. For example, a chromate treatment is carried out by immersion using a solution consisting of 200 g/L of a chromic anhydride, 20 g/L of sulfuric acid, and 10 g/L of NaF, at 50 to 60° C. for 1 to 3 minutes.

The plated product of the second embodiment has the following advantages.

(3) In the second embodiment, the plated product having a black trivalent chromium plating film in which nanodiamond particles are dispersed has a b* value of the surface thereof of four or less. Accordingly, the jet-black plated product having a trivalent chromium plating film obtains a reduced yellowish color.

(4) When the plated product of the second embodiment has an L* value of the surface of fifty or less, a black trivalent chromium plating film obtains a richer jet-black appearance.

The above described embodiment may be modified as follows.

The shape and purpose of use of an object to be plated (plated product) of the above embodiment are not particularly limited and can be suitably employed in the fields of interior or exterior parts for vehicles, electrical and electronic parts, and daily necessities.

In the second embodiment, the structure in which a copper plating layer, a semi-bright nickel plating layer, a bright nickel plating layer, and a microporous nickel plating layer are laminated as base plating layers has been described as an example, but is not limited to these metal plating layers. Metals or metal alloys such as Cu, Zn, Cr, Mo, Fe, Pb, Sn, and Ni are suitably selected to form a base plating layer. Additionally, the lamination sequence is not particularly limited.

In the above embodiment, an electroless nickel or copper plating treatment is applied as a pretreatment when an electroplating treatment is applied to an object to be plated, but a method other than such a plating treatment may be used.

In the above embodiment, the temperature and time for each plating treatment can be suitably determined in consideration of kind and productivity of an object to be plated.

It is not an intention to prevent the addition of inorganic particles such as colloidal silica, other than the nanodiamond as a color enhancer, to the above electroplating bath within a range that does not inhibit the advantages of the present disclosure. When colloidal silica is used in combination, a yellowish color (b* value) is more reduced. However, it is preferable not to use colloidal silica in combination from the viewpoint of more reducing lightness (L* value).

EXAMPLES

Next, the embodiments will be described further specifically with reference to Examples and Comparative Examples. However, the configuration of the present disclosure is not limited to the configuration of each Example.

Test Example 1: Evaluation Test on Appearance Characteristics of a Plated Product to which a Plating Treatment is Applied

An object to be plated, to which a base plating treatment shown below was applied, was prepared. A trivalent chromium plating treatment using an electroplating bath of each Example was carried out and an obtained plated product of each Example was evaluated for appearance characteristics (yellowish color, lightness).

Object to be Plated

A base plating treatment was carried out onto an ABS plastic to which conductivity was imparted by a pretreatment. The base plating treatment was carried out by immersing the conductive ABS plastic substrate in various metal plating baths according to a routine method so that a copper plating layer, a semi-bright nickel plating layer, a bright nickel plating layer, and a microporous nickel plating layer were sequentially laminated.

Example 1

A 2.5 mL/L of a uDiamond plating additive dispersion (primary particle 4 to 6 nm) manufactured by Carbodeon was added as the nanodiamond to a plating bath base solution (agent B was not used, 5 mL/L of agent D, and 40 mL/L of agent K) for trivalent chromium plating shown in Table 1 so that an amount of nanodiamond was 0.05 g/L in the plating bath. The base plating-treated object to be plated was subjected to the trivalent chromium plating treatment under the conditions shown in Table 2 and nanodiamond particles were coprecipitated.

Subsequently, the plating-treated product, to which the trivalent chromium plating treatment was applied, was further subjected to a chromate treatment. The chromate treatment was carried out using ECR500 (manufactured by JUC) according to a routine method. The obtained chromate plating-treated object (plated product) was evaluated on the surface appearance for the obtainment of bright appearance according to the criteria shown below. Additionally, the values of L* and b* at the surface were respectively measured using a spectrophotometer (manufactured by Konica Minolta, Inc.: CM-700D). Results are shown in Table 3.

TABLE 1 Amount used Composition Agent A 150 mL/L Chromium sulfate Agent B Amount used as in Silicon dioxide (colloidal Table 3 silica) Agent D Amount used as in Sodium thiocyanate Table 3 Agent G 30 mL/L Sulfuric acid Agent J 4 mL/L Cobalt sulfate Agent K 40 mL/L or 80 mL/L Arginine (Arg), histidine (His) Agent S 280 g/L Potassium sulfate, boric acid Agent W 1.5 mL/L Dipentyl sulfosuccinate

TABLE 2 Amount of solution 300 mL Solution temperature 40° C. Plating bath pH 3.2 Agitation Air agitation Current density 7 A/dm²

Examples 2 to 7

A procedure was carried out in the same manner as in Example 1 except that agent D, agent B, and nanodiamond (manufactured by Carbodeon: uDiamond plating additive dispersion) respectively in the amounts shown in Table 3 and 40 mL/L of agent K were used. Results are shown in Table 3, respectively.

Examples 8, 9

A procedure was carried out in the same manner as in Example 1 except that agent D, agent B, and nanodiamond (manufactured by Carbodeon: uDiamond plating additive dispersion) respectively in the amounts shown in Table 3 and 80 mL/L of agent K were used. Results are shown in Table 3, respectively.

Comparative Example 1

A procedure was carried out in the same manner as in Example 1 except that a trivalent chromium plating bath with which agent D in the amount shown in Table 3 and 40 mL/L of agent K were blended, and agent B and nanodiamond was not blended was used. Results are shown in Table 3.

Comparative Example 2

A procedure was carried out in the same manner as in Example 1 except that a trivalent chromium plating bath with which agent D and agent B in the amounts shown in Table 3 and 40 mL/L of agent K were blended, and nanodiamond was not blended was used. Results are shown in Table 3.

Comparative Example 3

A procedure was carried out in the same manner as in Example 1 except that a trivalent chromium plating bath with which agent D in the amount shown in Table 3 and 40 mL/L of agent K were blended, and nanodiamond was not blended but further 4 mL/L of agent B, in which colloidal silica is replaced with TiO₂ particles (average particle size 7 nm), was blended. TiO₂ particle was in the same concentration as the colloidal silica in agent B. The obtained chromate plating-treated product of Comparative Example 3 failed to obtain a desired bright appearance and thus was not measured for L* and b* values at the surface.

Bright appearance

-   -   ∘ Jet-black bright appearance was obtained.     -   x Jet-black bright appearance was not obtained.

TABLE 3 Nanodiamond Nanodiamond Agent D Agent B concentration concentration Bright L* b* (mL/L) (mL/L) (mass %) (g/L) appearance Value Value Example 1 5 0 0.005 0.05 ∘ 48.92 4.0 Example 2 5 0 0.01 0.1 ∘ 49.18 3.9 Example 3 5 0 0.1 1.0 ∘ 50.6 3.92 Example 4 5 0 0.2 2.0 ∘ 51.13 3.66 Example 5 5 0 0.4 4.0 ∘ 52.3 3.58 Example 6 5 4 0.4 4.0 ∘ 52.94 3.35 Example 7 5 6 0.4 4.0 ∘ 53.29 3.15 Example 8 5 0 0.005 0.05 ∘ 47.92 3.97 Example 9 5 0 0.01 0.1 ∘ 46.67 3.59 Comparative 5 0 0 0 ∘ 48.46 4.4 Example 1 Comparative 5 4 0 0 ∘ 49.28 4.21 Example 2 Comparative 5 TiO₂ 0 0 x — — Example 3

As shown in Table 3, in the configuration of each Example, a good jet-black bright appearance was obtained and a plating film with a reduced yellowish color (b* value) was also obtained. When a nanodiamond content was low (e.g., 0.1 g/L or less), a better jet-black bright appearance with not only a reduced yellowish color but also a low lightness (L* value) was obtained.

In Comparative Example 1, which did not contain the nanodiamond, and Comparative Example 2, in which colloidal silica was used in place of the nanodiamond, it was confirmed that the yellowish color at the surface was not reduced. Further, Comparative Example 3, in which a titanium oxide was used as the inorganic particle failed to obtain a jet-black bright appearance.

Various changes in form and details may be made to the examples above without departing from the spirit and scope of the claims and their equivalents. The examples are for the sake of description only, and not for purposes of limitation. Descriptions of features in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined differently, and/or replaced or supplemented by other components or their equivalents. The scope of the disclosure is not defined by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure. 

What is claimed is:
 1. An electroplating bath for precipitating a black trivalent chromium layer onto an object to be plated, the electroplating bath comprising a nanodiamond and a thiocyanate ion as color enhancers.
 2. The electroplating bath according to claim 1, wherein a concentration of the nanodiamond is 0.02 to 0.16 g/L.
 3. A method for manufacturing a plated product having a black trivalent chromium plating film, comprising: forming a black trivalent chromium plating film onto an object to be plated by electroplating using the electroplating bath according to claim 1; and applying a chromate treatment onto the black trivalent chromium plating film.
 4. A plated product having a black trivalent chromium plating film in which nanodiamond particles are dispersed, wherein a b* value of a surface of the plated product is four or less.
 5. The plated product according to claim 4, wherein an L* value of the surface of the plated product is fifty or less. 